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-   -   Mesh quality after snappyHex (http://www.cfd-online.com/Forums/openfoam-meshing-snappyhexmesh/117355-mesh-quality-after-snappyhex.html)

Pj. May 7, 2013 04:59

Mesh quality after snappyHex
 
Hi,

i'm running the case of a flow inside a rough channel. I'm trying to generate a proper mesh. The bottom roughness is formed by small cubical blocks.

Each block's surface mesh should be formed by approximately 4 cells in the vertical direction and 2 cells in the two horizontal directions (although the refined cells should be about 2.5 units wide, while the blocks are 4.5 units wide, so a BIT LESS than 2 cells).

After snappyHex, however, i ran checkMesh and the result is the following
Code:

Checking topology...
    Boundary definition OK.
    Cell to face addressing OK.
    Point usage OK.
    Upper triangular ordering OK.
    Face vertices OK.
    Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces ...
    Patch              Faces    Points  Surface topology                 
    in                  6410    6743    ok (non-closed singly connected) 
    out                5600    5781    ok (non-closed singly connected) 
    left                18367    19132    ok (non-closed singly connected) 
    right              18367    19132    ok (non-closed singly connected) 
    top                56000    56541    ok (non-closed singly connected) 
    bottom              510205  595645  ok (non-closed singly connected) 
    spires_patch0      46711    48691    ok (non-closed singly connected) 
    roughness_patch0    603177  690348  ok (non-closed singly connected) 
    hangar_patch0      38240    38481    ok (non-closed singly connected) 

Checking geometry...
    Overall domain bounding box (-10 -7 -0.00139171) (30 7 4)
    Mesh (non-empty, non-wedge) directions (1 1 1)
    Mesh (non-empty) directions (1 1 1)
    Boundary openness (3.74041e-16 1.31646e-15 -1.22914e-13) OK.
    Max cell openness = 4.21681e-16 OK.
    Max aspect ratio = 5.83191 OK.
    Minumum face area = 1.76458e-05. Maximum face area = 0.0200125.  Face area magnitudes OK.
    Min volume = 6.93409e-07. Max volume = 0.00200123.  Total volume = 2237.84.  Cell volumes OK.
    Mesh non-orthogonality Max: 57.4584 average: 12.2611
    Non-orthogonality check OK.
 ***Error in face pyramids: 7 faces are incorrectly oriented.
  <<Writing 7 faces with incorrect orientation to set wrongOrientedFaces
 ***Max skewness = 7.12497, 102 highly skew faces detected which may impair the quality of the results
  <<Writing 102 skew faces to set skewFaces

    Coupled point location match (average 0) OK.

How can i improve the result?

I don't know if these informations are enough. If you need to know more i can post some screenshots or others dicts.

Thank you very much

Akshay May 10, 2013 05:39

Hey Luca

Firstly check where these cells are located. Use foamToVTK -faceSet to write them in the vtk format and use paraview to view them. Then think of ways to refine those areas to get a better mesh.

Ak

Pj. May 15, 2013 00:46

Thanks Akshay. I will try this way


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